Tough new federal rules aimed at limiting smog, proposed last week by the Obama administration, could lead to changes in everything from what kind of gas is sold around Tampa Bay to whether mass transit gets a big push to what kind of suburban development is allowed, state and county officials say.

"It's a long lead time," said state Department of Environmental Protection Secretary Mike Sole.

The U.S. Environmental Protection Agency is targeting two chemicals that on sunny summer days combine to produce ozone, the main ingredient of smog: hydrocarbons and nitrogen oxide. Both puff out of the tailpipes of cars, trucks and motorcycles, as well as coal-burning power plants and industrial smokestacks.

The ozone limit currently enforced by U.S. Environmental Protection Agency under the Clean Air Act — a limit set by the Clinton administration in 1997 — was 84 parts per billion (ppb) over an eight-hour period. However, studies show that more people head to hospitals with respiratory problems when ozone increases.

So the American Lung Association sued the EPA, demanding it set a more stringent standard. The EPA turned to a science advisory panel, which unanimously recommended setting the limit no higher than 70 ppb, and urged the EPA to consider one as tough as 60 ppb.

But electric utilities, oil companies and other businesses lobbied the agency to keep the standard where it was, arguing that tighter regulations would cost too much. Two years ago, the Bush administration attempted a compromise, setting a new ozone limit of 75 ppb.

The American Lung Association challenged that standard as well, arguing it lacked a proper scientific basis, and last year the Obama administration announced it would reconsider it. Last week, the EPA announced the new ozone limit will now be between 60 and 70 ppb — to be phased in over two decades.

The EPA looked 10 years out and projected that if the standard is 60 ppb, six Florida counties will flunk: Pinellas, Hillsborough and Manatee counties in the Tampa Bay region; and Escambia, Santa Rosa and Bay counties in the Panhandle. However, if the standard is higher, those counties may be in the clear, the EPA says.

Finding ways to comply with that 60 ppb standard could be difficult, state and county officials say. They could require a different kind of gasoline mixture be sold at area gas stations to limit smog-causing pollution, but there could be more sweeping changes, too. "It could put some new constraints on growth in some areas of Florida," said Peter Hessling, director of Pinellas County's air quality division. "You could see requirements for more mass transit and more pedestrian-friendly development."

Sole predicted that if the EPA pursues the toughest possible limit, it would give further fuel to the drive for increased mass transit around the state.

The EPA estimated that complying with the new requirements will cost industry and motorists from $19 billion to as much as $90 billion a year by 2020, while saving Americans up to $100 billion on respiratory health problems, including lost work days and the cost of hospital visits.

But first the new standards have to become official. First comes 60 days of public comment and public hearings. The EPA hopes to announce its final version of the rules in August.

Then the states get their turn. They have until next January to tell the EPA which counties will flunk the new standards. Then they face a deadline of December 2013 to produce a plan for bringing those counties into compliance.

The states then have still more time — anywhere from 2014 to 2031 — to put those plans into effect and meet the new standards.